Jim Kaufeld writes:

Anyway, the GEM has an intermittently flaky display. Sometimes it goes crazy
and the bar graphs and digital temp readouts start fluctuating wildly. It
isn't just one engine and it isn't just one cylinder. Its all of them.

Does this look familiar?
http://lairds.org/Kyler/photos/disk0024/mvi_1757.avi
(It got much worse than that.)

First verify that your engines are sufficiently grounded. Then
verify it again. Check your alternators while you're there.

Next see if you can isolate a bad probe (or probes) by flying with
some disconnected.

Good luck.

--kyler